Mimicking High-Silica Zeolites: Highly Stable Germanium- and Tin-Rich Zeolite-Type Chalcogenides

High-silica zeolites, as exemplified by ZSM-5, with excellent chemical and thermal stability, have generated a revolution in industrial catalysis. In contrast, prior to this work, high-silica-zeolite-like chalcogenides based on germanium/tin remained unknown, even after decades of research. Here six crystalline high-germanium or high-tin zeolite-type sulfides and selenides with four different topologies are reported. Their unprecedented framework compositions give these materials much improved thermal and chemical stability with high surface area (Langmuir surface area of 782 m²/g^–1) comparable to or better than zeolites. Among them, highly stable CPM-120-ZnGeS allows for ion exchange with diverse metal or complex cations, resulting in fine-tuning in porosity, fast ion conductivity, and photoelectric response. Being among the most porous crystalline chalcogenides, CPM-120-ZnGeS (exchanged with Cs⁺ ions) also shows reversible adsorption with high capacity and affinity for CO₂ (98 and 73 cm³ g^–1 at 273 and 298 K, respectively, isosteric heat of adsorption = 40.05 kJ mol^–1). Moreover, CPM-120-ZnGeS could also function as a robust photocatalyst for water reduction to generate H₂. The overall activity of H₂ production from water, in the presence of Na₂S–Na₂SO₃ as a hole scavenger, was 200 μmol h^–1/(0.10 g). Such catalytic activity remained undiminished under illumination by UV light for as long as measured (200 h), demonstrating excellent resistance to photocorrosion even under intense UV radiation

From Hemoglobin to Porous N–S–Fe-Doped Carbon for Efficient Oxygen Electroreduction

Nitrogen–sulfur–iron-doped porous carbon material with high surface area (1026 m² g^–1) and large pore size is synthesized by the pyrolysis of hemoglobin, an abundant and inexpensive natural compound, with mesoporous silica foam (MS) as a template and thiocarbamide (TCA) as an additional sulfur source in an argon atmosphere. Our results indicated that as compared to the commercial 20% Pt/C catalyst, the synthesized catalyst exhibits not only higher current density and stability but also higher tolerance to crossover chemicals. More importantly, the synthetic method is simple and inexpensive

Nonphotochemical Base-Catalyzed Hydroxylation of 2,6-Dichloroquinone by H₂O₂ Occurs by a Radical Mechanism

Kinetic and structural studies have shown that peroxidases are capable of the oxidation of 2,4,6-trichlorophenol (2,4,6-TCP) to 2,6-dichloro-1,4-benzoquinone (2,6-DCQ). Further reactions of 2,6-DCQ in the presence of H₂O₂ and OH^– yield 2,6-dichloro-3-hydroxy-1,4-benzoquinone (2,6-DCQOH). The reactions of 2,6-DCQ have been monitored spectroscopically [UV–visible and electron spin resonance (ESR)] and chromatographically. The hydroxylation product, 2,6-DCQOH, has been observed by UV–visible and characterized structurally by ¹H and ¹³C NMR spectroscopy. The results are consistent with a nonphotochemical base-catalyzed oxidation of 2,6-DCQ at pH > 7. Because H₂O₂ is present in peroxidase reaction mixtures, there is also a potential role for the hydrogen peroxide anion (HOO^–). However, in agreement with previous work, we observe that the nonphotochemical epoxidation by H₂O₂ at pH < 7 is immeasurably slow. Both room-temperature ESR and rapid-freeze-quench ESR methods were used to establish that the dominant nonphotochemical mechanism involves formation of a semiquinone radical (base -catalyzed pathway), rather than epoxidation (direct attack by H₂O₂ at low pH). Analysis of the kinetics using an Arrhenius model permits determination of the activation energy of hydroxylation (<i>E</i>_a = 36 kJ/mol), which is significantly lower than the activation energy of the peroxidase-catalyzed oxidation of 2,4,6-TCP (<i>E</i>_a = 56 kJ/mol). However, the reaction is second order in both 2,6-DCQ and OH^– so that its rate becomes significant above 25 °C due to the increased rate of formation of 2,6-DCQ that feeds the second-order process. The peroxidase used in this study is the dehaloperoxidase-hemoglobin (DHP A) from Amphitrite ornata, which is used to study the effect of a catalyst on the reactions. The control experiments and precedents in studies of other peroxidases lead to the conclusion that hydroxylation will be observed following any process that leads to the formation of the 2,6-DCQ at pH > 7, regardless of the catalyst used in the 2,4,6-TCP oxidation reaction